1. Field of the Invention
The present invention relates to a heating apparatus using induction heating, and in particular, to a fixing apparatus available for a copying apparatus, a printer apparatus or the like which is an electrophotographic system using a thermal melting image developing agent, the fixing apparatus fixing the image developing agent on a recording object.
2. Description of the Related Art
A fixing apparatus built into a copying apparatus using an electrophotographic process heats and melts toner (image developing agent) formed on a fixing material (recording material), and fixes the toner to the recording material. In recent years, induction heating has been widely used as a heating method in which a heating time, which is a time from the point in time when electric power supply is started until the time when it reaches a fixable temperature, can be reduced. Further, there is a report in which the characteristic of a roller (or belt) as one of the factors by which a heating time can be reduced.
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-295452, a roller having elasticity and adiathermancy, and a heating apparatus using the roller are shown. As the feature of the heating apparatus disclosed in this document, there is shown that the starting of heating is fast (a time from the point in time when electric power supply is started until the time when a fixable temperature is reached).
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-213434, a heating apparatus is shown in which toner fixed on a recording paper is hardly stripped off. As the feature of the heating apparatus disclosed in this document, there is shown that a contact length between a heating roller and a pressure roller in the direction in which the recording paper is conveyed, i.e., a nip width, is made sufficiently large.
However, even when the heating apparatuses shown in the two documents described above are used, heat generated at the conductor layer portion is not necessarily sufficient for fixing toner to a recording material due to a material of a core material of a roller, i.e., a rotator, or a distance between the core material and a conductor layer (fixing surface) of the surface. Further, there is verified that a rise in the temperature of the core material which does not contribute to a rise in the temperature of the fixing surface.